ABSTRACT
Hypoxia serves as a physiologic cue to drive an angiogenic response via HIF-dependent mechanisms. Interestingly, minor elevation of lactate levels in the tissue produces the same effect under aerobic conditions. Aerobic glycolysis contributes to lactate accumulation in the presence of oxygen, especially under inflammatory conditions. We previously postulated that aerobic lactate accumulation, already known to stimulate collagen deposition, will also stimulate angiogenesis. If substantiated, this concept would advance understanding of wound healing and aerobic angiogenesis because lactate accumulation has many aerobic sources. In this study, Matrigel plugs containing a powdered, hydrolyzable lactate polymer were implanted into the subcutaneous space of mice. Lactate monomer concentrations in the implant were consistent with wound levels for more than 11 days. They induced little inflammation but considerable VEGF production and were highly angiogenic, as opposed to controls. Arterial hypoxia abrogated angiogenesis. Furthermore, inhibition of lactate dehydrogenase by using oxamate also prevented the angiogenic effects of lactate. Lactate monomer, at concentrations found in cutaneous wounds, stabilized HIF-1alpha and increased VEGF levels in aerobically cultured human endothelial cells. Accumulated lactate, therefore, appears to convey the impression of "metabolic need" for vascularization, even in well-oxygenated and pH-neutral conditions. Lactate and oxygen together stimulate angiogenesis and matrix deposition.
Subject(s)
Lactates/metabolism , Neovascularization, Physiologic , Oxidation-Reduction , Animals , Collagen/chemistry , Drug Combinations , Female , Hydrolysis , Hypoxia , Hypoxia-Inducible Factor 1, alpha Subunit/metabolism , Inflammation , L-Lactate Dehydrogenase/metabolism , Laminin/chemistry , Mice , Oxygen/metabolism , Proteoglycans/chemistry , Proto-Oncogene Proteins c-kit/biosynthesis , Vascular Endothelial Growth Factor A/metabolismABSTRACT
The significance of the high lactate levels that characterize healing wounds is not fully understood. Lactate has been shown to enhance collagen synthesis by fibroblasts and vascular endothelial growth factor (VEGF) production by macrophages and endothelial cells. VEGF has been shown to induce endothelial cell migration. However, it has not been shown whether accumulated lactate correlates with the biological activity of VEGF. Therefore, we investigated the effect of lactate on migration of endothelial cells. Human umbilical vein endothelial cells and human microvascular endothelial cells were cultured to subconfluent monolayers in standard six-well tissue culture plates. Following a 24-hour serum starvation, cells were treated with the indicated concentrations of l-lactate. Cell migration was assessed using a modified Boyden chamber. VEGF protein in the cell culture supernatant was measured by enzyme-linked immunoassay. Lactate-enhanced VEGF protein synthesis in a time- and dose-dependent manner. Lactate added into the bottom well did not stimulate cellular migration from the upper well. However, lactate when added together with endothelial cells to the bottom well of the Boyden chamber increased cellular migration in a dose-dependent manner. This effect was blocked by anti-VEGF and by cycloheximide. Lactate enhances VEGF production in endothelial cells, although lactate, itself, is not a chemoattractant. We conclude that the lactate-mediated increase in cellular migration is regulated by VEGF.
